ELECTRIC CURRENT A flow of electric charges is

¸üµÖŸÖ ׿Ö� Ö� Ö ÃÖÓãÖÖ, � ú´ÖÔ¾Ö߸ü ×¾ÖªÖ¯ÖϲÖÖê×¬Ö Öß, ´Ö¬µÖ ×¾Ö³ÖÖ� Ö, ÃÖÖŸÖÖ¸üÖ ELECTRIC CURRENT A flow of electric charges is called s electric current Std-8 th Chap. -Electric current. Sub-Science.

¸üµÖŸÖ ׿Ö� Ö� Ö ÃÖÓãÖÖ, � ú´ÖÔ¾Ö߸ü ×¾ÖªÖ¯ÖϲÖÖê×¬Ö Öß, ´Ö¬µÖ ×¾Ö³ÖÖ� Ö, ÃÖÖŸÖÖ¸üÖ DRY CELL • Outer covering of the cell is made of the zinc [zn] and acts as the negative [-] pole of the cell. • Carbon rod acts as the positive pole of the cell. s • Around it is a mixture of finely powedered manganese dioxide [Mno 2] and graphite [c] held in a bag of thin material. • The space between this bag and the outer cylindrical zinc Std-8 th Chap. -Electric current. Sub-Science.

¸üµÖŸÖ ׿Ö� Ö� Ö ÃÖÓãÖÖ, � ú´ÖÔ¾Ö߸ü ×¾ÖªÖ¯ÖϲÖÖê×¬Ö Öß, ´Ö¬µÖ ×¾Ö³ÖÖ� Ö, ÃÖÖŸÖÖ¸üÖ Is filled with a moist paste of zink chloride [zncl 2] and ammonium chloride [nh 4 cl]. then, the carbon rod is fitted with a metal s cap and the cell is sealed. Std-8 th Chap. -Electric current. Sub-Science.

¸üµÖŸÖ ׿Ö� Ö� Ö ÃÖÓãÖÖ, � ú´ÖÔ¾Ö߸ü ×¾ÖªÖ¯ÖϲÖÖê×¬Ö Öß, ´Ö¬µÖ ×¾Ö³ÖÖ� Ö, ÃÖÖŸÖÖ¸üÖ • SIMPLE Cell- the figure shows that a simple electric cell is connected in an electric cell. • In a trough a plate of zinc [zn] and plate of copper [cu] are stand some distance apart. • The zink plate acts as the negative [-] pole and the copper plate as the positive poleof the cell. s • The circuit includes a bulb and a key which can be opened or closed • The elecric current can be started or stopped by closing or opening the key. this cell is called a volta’s cell. Std-8 th Chap. -Electric current. Sub-Science.

¸üµÖŸÖ ׿Ö� Ö� Ö ÃÖÓãÖÖ, � ú´ÖÔ¾Ö߸ü ×¾ÖªÖ¯ÖϲÖÖê×¬Ö Öß, ´Ö¬µÖ ×¾Ö³ÖÖ� Ö, ÃÖÖŸÖÖ¸üÖ LECLANCHE’S CELL. • In a cylindrical pot there is a mixture of manganese dioxide and carbon. • A carbon rod placed in it is acts as positive pole and a zinc rod is the nigative pole s • A solution of ammonium chloride is filled in a large glass container and the porous pot and the zinc rod are placed in it. • The chemical reaction between manganese dioxide , zinc and ammonium chloride causes an electric current to flow. Std-8 th Chap. -Electric current. Sub-Science.

¸üµÖŸÖ ׿Ö� Ö� Ö ÃÖÓãÖÖ, � ú´ÖÔ¾Ö߸ü ×¾ÖªÖ¯ÖϲÖÖê×¬Ö Öß, ´Ö¬µÖ ×¾Ö³ÖÖ� Ö, ÃÖÖŸÖÖ¸üÖ NICKEL CADMIUM CELL • Nickel cadmium cell is used in drilling machines or some gardening tools. v In this cell the cadmium acts as nigative pole and nickel is positive pole. s v The space between them is filled with the alkali potassium hydroxide. • The cell is made airtight to prevent the leakage and corrosion. • It can be recharged again and again. Std-8 th Chap. -Electric current. Sub-Science.

¸üµÖŸÖ ׿Ö� Ö� Ö ÃÖÓãÖÖ, � ú´ÖÔ¾Ö߸ü ×¾ÖªÖ¯ÖϲÖÖê×¬Ö Öß, ´Ö¬µÖ ×¾Ö³ÖÖ� Ö, ÃÖÖŸÖÖ¸üÖ THE BUTTON CELL • This cell is button shaped. • It is also called a lithium cell. • It has negative pole of lithium iron phosphate and a positive pole of carbon s • The space between them is filled with a lithium salt. • This cell does not leak. • It cannot be recharged. Std-8 th Chap. -Electric current. Sub-Science.

¸üµÖŸÖ ׿Ö� Ö� Ö ÃÖÓãÖÖ, � ú´ÖÔ¾Ö߸ü ×¾ÖªÖ¯ÖϲÖÖê×¬Ö Öß, ´Ö¬µÖ ×¾Ö³ÖÖ� Ö, ÃÖÖŸÖÖ¸üÖ THE MAGNETIC FIELD While an electric current flowes through a conductor it behaves like a magnet. s Hence a magnetic field developes around it, which causes the deflection of the needle. Std-8 th Chap. -Electric current. Sub-Science.

¸üµÖŸÖ ׿Ö� Ö� Ö ÃÖÓãÖÖ, � ú´ÖÔ¾Ö߸ü ×¾ÖªÖ¯ÖϲÖÖê×¬Ö Öß, ´Ö¬µÖ ×¾Ö³ÖÖ� Ö, ÃÖÖŸÖÖ¸üÖ ELECTRO MAGNETIC INDUCTION • If there is change in the magnetic field associated with a coil of wire , elecric s current begins to flow through the coil. Such a current is called an induced current. Std-8 th Chap. -Electric current. Sub-Science.